Glucose

General

Common Use:To assist in the diagnosis of diabetes and to evaluate disorders of carbohydrate metabolism such as malabsorption syndrome.

Specimen:Serum collected in a gold-, red-, or red/gray-top tube, although plasma is recommended for diagnosis of diabetes. Plasma collected in a gray-top (sodium fluoride) or a green-top (heparin) tube.

Normal Findings:(Method: Spectrophotometry)

Age

Conventional Units

SI Units (Conventional Units × 0.0555)

Fasting

Cord blood

45–96 mg/dL

2.5–5.3 mmol/L

Premature infant

20–80 mg/dL

1.1–4.4 mmol/L

Newborn 2 d–2 yr

30–100 mg/dL

1.7–5.6 mmol/L

Child

60–100 mg/dL

3.3–5.6 mmol/L

Adult-older adult

Less than 100 mg/dL

Less than 5.6 mmol/L

Prediabetes or impaired fasting glucose

100–125 mg/dL

5.6–6.9 mmol/L

2-hr postprandial

65–139 mg/dL

3.6–7.7 mmol/L

Prediabetes or impaired 2-hr sample

140–199 mg/dL

7.8–11 mmol/L

Random

Less than 200 mg/dL

Less than 11.1 mmol/L

The American Diabetes Association and National Institute of Diabetes and Digestive and Kidney Diseases consider a confirmed fasting blood glucose greater than 126 mg/dL to be consistent with a diagnosis of diabetes. Values tend to increase in older adults.

Description

Glucose, a simple six-carbon sugar (monosaccharide), enters the diet as part of the sugars sucrose, lactose, and maltose and from the complex polysaccharide, dietary starch. The body acquires most of its energy from the oxidative metabolism of glucose. Excess glucose is stored in the liver or in muscle tissue as glycogen. Glucose levels in plasma (one of the components of blood) are generally 10% to 15% higher than glucose measurements in whole blood (and even more after eating). This is important because home blood glucose meters measure the glucose in whole blood, whereas most laboratory tests measure the glucose in either plasma or serum.

Diabetes is a group of diseases characterized by hyperglycemia, or elevated glucose levels. Hyperglycemia results from a defect in insulin secretion due to destruction of the beta cells of the pancreas (type 1 diabetes), a defect in insulin action, or a combination of defects in secretion and action (type 2 diabetes). The chronic hyperglycemia of diabetes over time may lead to damage, dysfunction, and eventually failure of the eyes (retinopathy), kidneys (nephropathy), nerves (neuropathy), heart (cardiovascular disease), and blood vessels (microvascular and macrovascular conditions). The American Diabetes Association (ADA) and National Institute of Diabetes and Digestive and Kidney Disease have established criteria for diagnosing diabetes to include any combination of the following findings or confirmation of any of the individual findings by repetition of the same test on a subsequent day:

An A1C(glycated hemoglobin) in adults equal to or greater than 6.5% (assumes the use of a standardized test as referenced to the National Glycohemoglobin Standardization Program—Diabetes Control and Complications Trial and the absence of clinical conditions such as hemoglobinopathies, anemias, and kidney and liver diseases known to affect the accuracy of the test results)

Glucose measurements have been used for many years as an indicator of short-term glycemic control to identify diabetes and assist in management of the disease. Glycated hemoglobin, or hemoglobin A1c, is used to indicate long-term glycemic control over a period of 3 to 4 months and is used as a diagnostic tool in the diagnosis of type 2 diabetes. The estimated average glucose (eAG) is a mathematical relationship between hemoglobin A1c and glucose levels expressed by the formula eAG = (mg/dL) = [(A1c × 28.7) – 46.7]For example, eAG for a patient with an A1c of 6% would be calculated as [(6 × 28.7) – 46.7] = 125.5 mg/dL. Studies have documented the need for markers that reflect intermediate glycemic control, or the period of time between 2 to 4 wk as opposed to hours or months. Many patients who appear to be well controlled according to glucose and A1c values actually have significant postprandial hyperglycemia. Management of postprandial hyperglycemia is considered to be extremely important in preventing or delaying the development of diabetes-related complications. The GlycoMark assay measures serum 1,5-anhydroglucitol is a validated marker of short-term glycemic control and can be used in combination with glucose and hemoglobin A1C measurements to provide a more complete picture of glucose levels over time. GlycoMark values greater than 8 mcg/mL are considered normal for adults. Serum 1,5-anhydroglucitol is a naturally occurring monosaccharide found in most foods. It is not normally metabolized by the body and is excreted by the kidneys. During periods of normal glucose levels, there is an equilibrium between glucose and 1,5-anhydroglucitol concentrations. When blood glucose concentration rises above 180 mg/dL (SI = 10 mmol/L), the renal threshold for glucose, levels of circulating serum 1,5-anhydroglucitol decrease due to competitive inhibition of renal tubular absorption favoring glucose over serum 1,5-anhydroglucitol. As glucose is retained in the circulating blood and levels of glucose increase, correspondingly higher amounts of 1,5-anhydroglucitol are excreted in the urine resulting in lower serum concentrations. The change in serum 1,5-anhydroglucitol levels is directly proportional to the severity and frequency of hyperglycemic episodes. Serum 1,5-anhydroglucitol concentration returns to normal after 2 wk with no recurrence of hyperglycemia. Reports from the medical community indicate that over half of the U.S. population will have diabetes or prediabetes by 2020. The combined use of available markers of glycemic control will greatly improve the ability to achieve tighter, more timely glycemic control.

Comparison of Markers of Glycemic Control to Approximate Blood Glucose Concentration

1,5–Anhydroglucitol Measured Using the GlycoMark Assay

Hemoglobin A1c

Estimated Blood Glucose (mg/dL)

Degree of Diabetic Control

14 mcg/mL or greater

4%–5%

68–97 mg/dL

Normal/nondiabetic

10–12 mcg/mL

4%–6%

68–126 mg/dL

Well controlled

5–10 mcg/mL

6%–8%

126–183 mg/dL

Moderately well controlled

2–5 mcg/mL

8%–10%

183–240 mg/dL

Poorly controlled

Less than 2 mcg/mL

Greater than 10% (11%–14%)

269–355 mg/dL

Very poorly controlled

Assessment of medications used to manage diabetes is an important facet of controlling the disease and its health-related complications. Drug response is an active area of study to ensure that the medications prescribed are meeting the needs of the patients who are taking them. Insulin and metformin are two commonly prescribed medications for the treatment of diabetes. See the “Insulin Antibodies” study for more detailed information. The AccuType Metformin Assay is a genetic test that identifies individuals who may not respond appropriately or who have a suboptimal response to metformin related to a genetic mutation in the proteins responsible for transporting metformin.

Glycogen storage diseases (deficiencies in enzymes involved in conversion of glycogen to glucose)

Hereditary fructose intolerance (inherited disorder of fructose metabolism; phosphates needed for intermediate steps in gluconeogenesis are trapped from further action by the enzyme deficiency responsible for fructose metabolism)

Hypopituitarism (decreased levels of hormones such as adrenocorticotropic hormone [ACTH] and GH result in decreased glucose levels)

Note and immediately report to the requesting health-care provider (HCP) any critical findings and related symptoms. A listing of these findings varies among facilities. Timely notification of a critical finding for laboratory or diagnostic studies is a role expectation of the professional nurse. The notification processes vary among facilities. Upon receipt of the critical finding, the information should be read back to the caller to verify accuracy.

Consideration may be given to verification of critical findings before action is taken. Policies vary among facilities and may include requesting immediate recollection and retesting by the laboratory or retesting using a rapid point-of-care testing instrument at the bedside, if available.

Glucose monitoring is an important measure in achieving tight glycemic control. The enzymatic GDH-PQQ test method may produce falsely elevated results in patients who are receiving products that contain other sugars (e.g., oral xylose, parenterals containing maltose or galactose, and peritoneal dialysis solutions that contain icodextrin). The GDH-NAD, glucose oxidase, and glucose hexokinase methods can distinguish between glucose and other sugars.

Administration of insulin or oral hypoglycemic drugs within 8 hr of a fasting blood glucose can lead to falsely decreased values.

Specimens should never be collected above an IV line because of the potential for dilution when the specimen and the IV solution combine in the collection container, falsely decreasing the result. There is also the potential of contaminating the sample with the substance of interest, if it is present in the IV solution, falsely increasing the result.

Failure to follow dietary restrictions before the procedure may cause the procedure to be canceled or repeated; failure to follow dietary restrictions before the fasting test can lead to falsely elevated glucose values.

Assess the patient’s ability to and prior efforts to manage the disease process; evaluate the ability to self-manage the disease, including blood glucose screening, dietary management, exercise, and medication self-administration; assess for personal factors that may limit the patient’s ability to self-perform, such as visual, cognitive, and hearing; assess the financial ability to purchase the medication and supplies necessary to provide self-care; assess the level of family support; ensure the patient has the adequate knowledge to perform self-care, and if not, provide the necessary training; ensure the patient knows the signs and symptoms related to the disease process; teach correct dietary selections meeting cultural- and age-appropriate needs; refer to social services or home health care; discuss how to manage diabetes during travel

Obtain a history of the patient’s health concerns, symptoms, surgical procedures, and results of previously performed laboratory and diagnostic studies. Include a list of known allergens, especially allergies or sensitivities to latex.

Obtain a list of the patient’s current medications, including over-the-counter medications and dietary supplements (see Effects of Dietary Supplements online at DavisPlus).

Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.

Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.

Instruct the patient to fast for at least 8 hr before specimen collection and not to consume any caffeinated products or chew any type of gum before specimen collection for the fasting glucose test; these factors are known to elevate glucose levels.

Instruct the patient to follow the instructions given for 2-hr postprandial glucose test. Some HCPs may order administration of a standard glucose solution, whereas others may instruct the patient to eat a meal with a known carbohydrate composition.

Intratest

Potential Complications:N/A

Ensure that the patient has complied with dietary restrictions and other pretesting preparations prior to the fasting study, as instructed.

Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.

Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.

Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection online at DavisPlus. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.

Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.

Promptly transport the specimen to the laboratory for processing and analysis.

Post Test

Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.

Instruct the patient to resume usual diet, as directed by the HCP.

Nutritional Considerations: Increased glucose levels may be associated with diabetes. There is no “diabetic diet”; however, many meal-planning approaches with nutritional goals are endorsed by the ADA Patients who adhere to dietary recommendations report a better general feeling of health, better weight management, greater control of glucose and lipid values, and improved use of insulin. Instruct the patient, as appropriate, in nutritional management of diabetes. A variety of dietary patterns are beneficial for people with diabetes. The Mediterranean-style diet emphasizes inclusion of vegetables, whole grains, fruits, low-fat dairy, nuts, legumes, and nontropical vegetable oils (e.g., olive, canola, peanut, sunflower, flaxseed) along with fish and lean poultry. A similar dietary pattern known as the Dietary Approaches to Stop Hypertension (DASH) diet makes additional recommendations for the reduction of dietary sodium. Both dietary styles emphasize a reduction in consumption of red meats, which are high in saturated fats and cholesterol, and other foods containing sugar, saturated fats, trans fats, and sodium. A vegetarian diet as well as other potential weight loss diets such as Weight Watchers are also supported by the ADA If triglycerides also are elevated, the patient should be advised to eliminate or reduce alcohol. The nutritional needs of each patient with diabetic patient need to be determined individually (especially during pregnancy) with the appropriate HCPs, particularly professionals educated in nutrition.

Social and Cultural Considerations: Numerous studies point to the prevalence of excess body weight in American children and adolescents. Experts estimate that obesity is present in 25% of the population aged 6 to 11 yr. The medical, social, and emotional consequences of excess body weight are significant. Special attention should be given to instructing the pediatric patient and caregiver regarding health risks and weight control education.

Social and Cultural Considerations: Studies comparing risk for developing diabetes demonstrate that certain populations are disproportionately affected by type 2 diabetes and complications of type 2 diabetes as compared to the general population. Nonmodifiable risk factors include age, ethnicity, and family history of diabetes or metabolic syndrome. The risk of developing type 2 diabetes increases with age. In the United States, affected populations include African Americans, Asian Americans, Hispanics, native Hawaiians and Pacific Islanders, American Indians, and Alaska natives. Modifiable risk factors include lifestyle choices related to making healthy dietary choices, maintaining a healthy body weight, and meeting recommended levels of physical activity. The financial and emotional burdens of diabetes and related complications continue to grow at an alarming rate. A system for the prevention, management, and support of patients with type 2 diabetes should be provided through the coordinated efforts of multidisciplinary partners using strategies that are culturally appropriate.

Recognize anxiety related to test results, and be supportive of perceived loss of independence and fear of shortened life expectancy. The ADA recommends A1C testing four times a year for insulin-dependent type 1 or type 2 diabetes when glycemic targets are not being met or when therapy has changed and twice a year when treatment goals are being met for non–insulin-dependent type 2 diabetes. The ADA also recommends that testing for diabetes commence at age 45 for asymptomatic individuals, be considered for adults of any age who are overweight and have additional risk factors, and continue every 3 yr in the absence of symptoms.

Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

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